Some time ago i switched from Ubuntu to Windows XP (in my work computer), mostly because it made my work easier and faster ,but i always missed the linux command line and all the tools. I tried Cygwin, it's not too bad but still is not Linux. Yesterday a co-worker (Ruben) showed me coLinux:

From the coLinux site:

Cooperative Linux is the first working free and open source method for optimally running Linux on Microsoft Windows natively. More generally, Cooperative Linux (short-named coLinux) is a port of the Linux kernel that allows it to run cooperatively alongside another operating system on a single machine.

In short words, it's like Vmware, Parallels, Virtual PC but free, lighter and faster. It take just 4 seconds to boot a debian sarge!!

So now i have a real full linux in my Windows environment :)

Right now there are available Debian, Fedora, Gentoo, Ubuntu, Mandrake and many more OS images.

Best of all you can start coLinux machine as a Windows service an access via SSH through your favorite Terminal emulator (Poderosa, Putty, etc).